1. Field of the Invention
The invention relates to a structure of a multi-input multi-output multicarrier code division multiple access (MIMO MC-CDMA) communication system and a communication method thereof, and more particularly, to a structure of a MIMO MC-CDMA communication system and a communication method using the space time block encoding technology and the space-path spreading codes.
2. Description of the Prior Art
Application of the network and communication system is changed from transferring text and audio data to transferring multimedia data, so the requirement of wireless bandwidth is getting more imperative. The multicarrier code division multiple access (MC-CDMA) communication system is a method to apply the spreading technology onto the OFDM structure. The MC-CDMA allows the spreading code to be independently modified on the carrier wave by the user to decline and flatten the channel, and provides the benefit of various frequencies against interference by using the first-order equalizer.
In the field of the wireless communication system, one of the most important topics is how to eliminate the decay and interference of signals, and a multi-input multi-output (MIMO) technology is disclosed recently. Pluralities of antennas are installed at both terminals of the wireless transmission, so the spectrum efficiency and transmission reliability can be obviously improved, and the diversity gain can be provided. In 1998, the BLAST (Bell Laboratories layered space-time) technology which is a structure of MIMO was disclosed by Foschini et al. (Wireless Personal Commun., vol. 6, pg.315-335). The spatial multiplexing function in the point-to-point narrow-band communication can be achieved with this technology without increasing transmitting power and system bandwidth. The spatial multiplexing function can transmit different data streams at pluralities of antennas simultaneously with the independent and parallel spatial channels, and get more effective spectrum of the communication system.
On the other hand, for improving the chain quality of the MIMO communication system, the transmit diversity and the receive diversity can be selected to obtain a flattened environment. For example, the space-time coding (STC) technology is a popular one used in the MIMO communication system. However, the spectrum efficiency and diversity cannot be simultaneously optimized, and can only choose one. For solving this problem, the multi-code transmission technology is developed, such as the space-time spreading BLAST (STS BLAST) technology. The technology disclosed by Huang et al. in the IEEE journal is one kind of the multi-code transmission technology (IEEE Trans. Wireless Commun., 2002 vol. 1, no. 3, pg. 383-392). However, when comparing with the method that only uses the BLAST technology or the space-time block coding (STBC) technology, the multi-code transmission technology can only get the lower spectrum efficiency and diversity gain. When applying to the wide-band system, or named the multiple path environment, the multi-code transmission efficiency will be lowered by the Intersymbol Interference (ISI) and the non-perpendicular substreams, and the conventional technologies cannot have a better diversity or spectrum efficiency.